The present invention relates to a power amplifying circuit to be used for a transmitting section of a base station or a terminal station of a radio communication system and a radio communication apparatus such as a mobile phone, and more particularly, to a distortion compensating device which compensates for non-linear distortion of an output signal of the power amplifying circuit.
In a transmission high-frequency power amplifying circuit (hereinafter referred to as power amplifying circuit) of a mobile phone or the like, if it is intended to increase power availability, non-linearity is intensified so that a distortion is generated in the output signal. As a distortion compensating device for compensating such a distortion, predistortion technology employing a compensating means having a characteristic inverse to the distortion of the power amplifying circuit has been well known.
Prior to description of the above described predistortion technology, principle about compensation of amplitude distortion will be described. The high-frequency signal which is an input signal to be considered now is a signal for use in the mobile phone, which is an orthogonal phase modulation signal such as xcfx80/4 shift QPSK (Quad Phase Shift Keying), 0-degree QPSK and the like subject to a band restriction. These signals can be expressed by a waveform obtained by amplitude-modulating high-frequency carrier components with envelope components changing slowly with the passage of time. This is expressed in an equation (1).
V=Vi(t)xc2x7cos(xcfx89t)xe2x80x83xe2x80x83(1) 
where V is a general expression of high-frequency signal voltage, Vi is the aforementioned envelope component, xcfx89 is an angular frequency of the high-frequency component. The signal expressed by the equation (1) is subjected to distortion when it is amplified by the power amplifying circuit 12 (see FIG. 11).
Although in the general power amplifying circuit 12, as shown in FIG. 4, the output power increases as the input power increases, its amplification factor decreases gradually. That is, gain suppression is generated, so that distortion is generated by this characteristic. When in an amplitude characteristic curve 21 of FIG. 4, the input power is a value indicated by A in FIG. 4, the output power is a value indicated by B. In this case, if the amplitude characteristic 22 of the power amplifying circuit 12 is linear, its output power must become Bxe2x80x2. Then, if the input power Axe2x80x2 is used instead of the input power A, its output power is Bxe2x80x2, so that by providing the input voltage with the non-linear distortion preliminarily, no distortion is generated in the output power. By converting input voltage A to input voltage Axe2x80x2 like this, the distortion becomes to be improved.
The technology of predistortion is an art for having the base band portion carry out an operation for converting this input voltage A to input voltage Axe2x80x2. Here, it should be noted that converting the input power A having no distortion originally to the input power Axe2x80x2 leads to adding the distortion to the input power A. This added distortion is killed by a distortion generated in the power amplifying circuit 12, so that it is considered that the distortion is improved. This added distortion acts like an inverted distortion with respect to a distortion generated in the power amplifying circuit 12.
FIG. 11 shows a block diagram about a typical predistortion well known since before. FIG. 11 will be described simply. FIG. 11 shows a transmitting portion of a mobile phone. Analog in-phase component I and orthogonal component Q generated in a signal processing portion 30 are digitalized by I and Q analog-digital converters (ADC) 31, 32 and then, the aforementioned operation for converting the input power A to the input power Axe2x80x2 is carried out by I- and Q-signal predistorters 33, 34. After that, the signals are converted to analog signals by I- and Q-signal digital-analog converters (DAC) 35, 36 and modulated by an orthogonal transformer 37. Then, it is converted to a high-frequency signal by an up-converter 38, amplified by a power amplifying circuit 12 and transmitted. If the predistortion is not carried out, the aforementioned ADCs 31, 32, the predistorters 33, 34 and the DACs 35, 36 in the base band portion 39 in the block shown in FIG. 11 are not necessary. That is, the predistortion conducts a signal conversion operation with respect to the original I, Q signals.
If the aforementioned predistortion is carried out, a signal provided with the inverted distortion component is outputted from the base band portion 39. However, in a general mobile phone, it is indispensable to provide a filter for removing digital noise contained in the base band output and a band-pass filter may be provided for an intermediate frequency portion also depending on the case. These filters cannot be removed in consideration of the purpose for which they are installed. It turns out that the inverted distortion component is removed together with the digital noise by this filter. As a result, the distortion in the power amplifying circuit 12 is not killed, so that the distortion compensation is not carried out.
A first distortion compensating device of the present invention is a distortion compensating device for carrying out predistortion with respect to a power amplifying means 12 whose distortion should be compensated, comprising: an envelope detecting means 1 to which a high-frequency signal S1 generating an envelope change is supplied for detecting an envelope signal of the high-frequency signal S1; an amplitude correction memory means 3 for storing an inverted distortion amplitude value of a distortion generated in the power amplifying means 12 with digital data S3 obtained by digitalizing the envelope signal S2 of the envelope detecting means 1 as an address; and a gain variable means 10 disposed in a prestage of the power amplifying means 12 to which the high-frequency signal S1 generating the envelope change is supplied, capable of controlling a passage gain of the high-frequency signal, characterized in that the inverted distortion data of the amplitude correction memory means 3 is converted to analog data and supplied to the gain variable means 10 so as to compensate a distortion of the amplitude of a gain of the power amplifying means 12.
A second distortion compensating device of the present invention is a distortion compensating device for carrying out predistortion on a power amplifying means 12 whose distortion should be compensated, comprising: an envelope detecting means 1 to which a high-frequency signal S1 generating an envelope change is supplied for detecting an envelope signal S2 of the high-frequency signal S1; a phase correction memory means 6 for storing an inverted distortion phase value of a distortion generated in the power amplifying means 12 with digital data S3 obtained by digitalizing the envelope signal S2 of the envelope detecting means 1 as an address; and a phase-shifting means 11 disposed in a prestage of the power amplifying means 12 to which the high-frequency signal S1 generating the envelope change is supplied, capable of controlling a passage phase of the high-frequency signal, characterized in that the inverted distortion data of the phase correction memory means 6 is converted to analog data and supplied to the phase-shifting means 11 so as to compensate a distortion of the phase of the power amplifying means 12.
A third distortion compensating device of the present invention is a distortion compensating device according to the first invention, further including; a phase correction memory means 6, parallel located with the amplitude correction memory means 3, which stores an inverted distortion phase value of distortion to be generated in the power amplifying means 12, with digital data S3 obtained by digitalizing the envelope signal S2 of the envelope detecting means 1 as an address; and a phase-shifting means 11 which can control passage phase of the high frequency signal by supplying analog data that the inverted distortion data of this phase correction memory means 6 is converted into an analog data, characterized in that the phase-shifting means 11 is connected with the gain variable means 10 in series at the prestage of the power amplifying means 12.
A fourth distortion compensating device of the present invention is a distortion compensating device according to the first or third invention characterized in that a delay means 9 for adjusting a difference of delay time between a main path having the power amplifying means 12 and the gain variable means 10 and a corrective control signal route having the envelope detecting means 1 for supplying a control signal to the gain variable means 10 and an amplitude correction memory means 3 is provided in the main path.
A fifth distortion compensating device of the present invention is a distortion compensating device according to the second or third invention characterized in that a delay means 9 for adjusting a difference of delay time between a main path having the power amplifying means 12 and the phase-shifting means 11 and a corrective control signal route having the envelope detecting means 1 for supplying a control signal to the phase-shifting means 11 and the phase correction memory means 6 is provided in the main path.
A sixth distortion compensating device of the present invention is a distortion compensating device according to the fourth or fifth invention characterized in that by detecting an envelope signal S14 from an output side of the power amplifying means 12 and feeding back a differential signal obtained by comparing this envelope signal S14 with an output of the envelope signal S2 from the envelope detecting means 1 to the delay means 9, the delay time is controlled.
A seventh distortion compensating device of the present invention is a distortion compensating device according to the first invention characterized in that an output obtained by comparing an output signal S14 as a result of envelope-detecting output of the power amplifying means 12 with an envelope signal S2 of the envelope detecting means 1 is digitalized. With this digital data serving as an address, a correction data memory means 17 for storing correction data for correcting a characteristic change by temperature is driven so as to multiply an output of the correction data memory means 17 by an output of the amplitude correction memory means 3, thereby compensating a change of the temperature characteristic of the power amplifying means 12.
An eighth distortion compensating device of the present invention is a distortion compensating device for carrying out predistortion on a power amplifying means 12 whose distortion should be compensated, comprising: an envelope detecting means 1 to which a high-frequency signal S1 generating an envelope change is supplied for detecting an envelope signal of a high-frequency signal S1; a phase correction memory means 6 for storing an inverted distortion phase value of a distortion generated in the power amplifying means 12 with digital data S3 obtained by digitalizing an envelope signal S2 of the envelope detecting means 1 as an address; and a phase-shifting means 11 disposed in a poststage of the power amplifying means 12 to which the high-frequency signal S1 generating the envelope change is supplied, capable of controlling a passage phase of the high-frequency signal S1, characterized in that inverted distortion data of the phase correction memory means 6 is converted to analog data and supplied to the phase-shifting means 11 so as to compensate a distortion of the phase of the power amplifying means 12.
A ninth distortion compensating device of the present invention is a distortion compensating device according to the eighth invention, further including: an amplitude correction memory means 3, parallel located with the phase correction memory means 6, which stores an inverted distortion amplitude value of distortion to be generated in the power amplifying means 12, with digital data S3 obtained by digitalizing the envelope signal of the envelope detecting means 1 as an address; and a gain variable means 10 which can control passage gain of the high frequency signal by supplying analog data that the inverted distortion data of this amplitude correction memory means 3 is converted into analog data, characterized in that the gain variable means 10 is connected at the prestage of the power amplifying means 12.
An eleventh distortion compensating device of the present invention is a distortion compensating device according to the tenth invention characterized in that by detecting an envelope signal S2 from an output side of the power amplifying means 12 and feeding back a differential signal obtained by comparing this envelope signal S12 with an envelope signal output S2 from the envelope detecting means 1 to the delay means 9, the delay time is controlled.
A twelfth distortion compensating device of the present invention is a distortion compensating device comprising: a first envelope detecting means 1 for detecting an envelope signal S2 with a part of a high frequency signal S1 having fluctuation of envelope as an input; a digital-to-analog converting means 2 for converting the envelope signal S2 of this first envelope detecting means 1 into digital data S3; an amplitude correction memory means 3 in which digital data S3 is inputted as an address and which outputs amplitude correction data S4 corresponding to the address by means of data stored for amplitude correction in advance; a first low pass filtering means 5 for converting amplitude correction data S4 into an analog signal to eliminate digital noise of an analog signal S5; a phase correction memory means 6 in which digital data S3 is inputted as an address and which outputs phase correction data S6 corresponding to the address by means of data stored for phase correction in advance; a second low pass filtering means 8 for converting phase correction data S6 into an analog signal to eliminate digital noise of an analog signal S7; a delay means 9 which can adjust the volume of delay of passing time by means of a control signal S16 to be added into a control terminal TC1 with the high frequency signal S1 as an input; a gain variable means 10 for varying a passage gain depending on the voltage of a signal S8 from the first low pass filtering means 5, to be added into a control terminal TC2 with a delay signal S10 of the delay means 9 as an input; a phase-shifting means 11 for varying a passage phase by an output signal S9 from the second low pass filtering means 8 with an output S11 of this gain variable means 10 as an input; to input a variable output signal into a power amplifying means 12 whose distortion should be compensated; a second envelope detecting means 13 for detecting an envelope signal S13 of an output of the power amplifying means 12 whose distortion should be compensated; a subtracting means 14 for detecting a difference between the envelope signal S2 and an envelope signal S14 with envelope signals S2 and S14 of the first and the second envelope detecting means 1, 13 as inputs; and a third low pass filtering means 15 for detecting only a DC signal S16 of this subtracting means 14, characterized in that the DC signal S16 of this third low pass filtering means 15 is fed back to the control terminal TC1 of the delay means 9.
A thirteenth distortion compensating device of the present invention is a distortion compensating device comprising: a first envelope detecting means 1 for detecting an envelope signal S1 with a part of a high frequency signal S1 having fluctuation of envelope as an input; a digital-to-analog converting means 2 for converting an envelope signal S2 of this first envelope detecting means 1 into digital data S3; an amplitude correction memory means 3 in which digital data S3 is inputted as an address and which outputs amplitude correction data S4 corresponding to the address by means of data stored for amplitude correction in advance; a first low pass filtering means 5 for converting amplitude correction data S4 into an analog signal to eliminate digital noise of an analog signal S5; a phase correction memory means 6 in which digital data S3 is inputted as an address and which outputs phase correction data corresponding to the address by means of data stored for phase correction in advance; a second low pass filtering means 8 for converting phase correction data into an analog signal S7 to eliminate digital noise of the analog signal S7; a delay means 9 which can adjust the volume of delay of passing time by means of a control signal to be added into a control terminal TC1 with the high frequency signal S1 as an input; a gain variable means 10 for varying a passage gain depending on the voltage of a signal S8 from the first low pass filtering means 5, to be added into a control terminal TC2 with a delay signal S10 of this delay means 9 as an input; a phase-shifting means 11 for varying a passage phase by means of an output signal S9 from the second low pass filtering means 8 by inputting an output S11 of this gain variable means 10 into a power amplifying means 12 whose distortion should be compensated and inputting an output S13 of the power amplifying means 12 thereinto; a second envelope detecting means 13 for detecting an envelope signal S14 of an output of this phase-shifting means 11; a subtracting means 14 for detecting a difference between the envelope signal S2 and the envelope signal S14 with envelope signals S2 and S14 of the first and the second envelope detecting means 1,13 as inputs; and a third low pass filtering means 15 for detecting only a DC signal S15 of this subtracting means 14, characterized in that the DC signal S11 of this third low pass filtering means 15 is fed back to the control terminal TC1 of the delay means 9.
A fourteenth distortion compensating device of the present invention is a distortion compensating device comprising: a first envelope detecting means 1 for detecting an envelope signal S1 with a part of a high frequency signal S1 having fluctuation of envelope as an input; a digital-to-analog converting means 2 for converting an envelope signal S2 of this first envelope detecting means 1 into digital data S3; an amplitude correction memory means 3 in which digital data S3 is inputted as an address and which outputs amplitude correction data corresponding to the address by means of data stored for amplitude correction in advance; a multiplying means 18 in which digital multiplier is the product with a digital output S4 of the amplitude correction memory means 3 as multiplicand; a first low pass filtering means 5 for converting digital data S19 of this multiplying means 18 to an analog signal S5 to eliminate digital noise of the analog signal S5; a phase correction memory means 6 in which digital data S3 is inputted as an address and which outputs phase correction data corresponding to the address by means of data stored for phase correction in advance; a second low pass filtering means 8 for converting phase correction data S6 into an analog signal S7 to eliminate digital noise of the analog signal S7; a delay means 9 which can adjust the volume of delay of passing time by means of a control signal S16 to be added into a control terminal TC1 with the high frequency signal S1 as an input; a gain variable means 10 for varying a passage gain depending on the voltage of a signal S8 from the first low pass filtering means 5, to be added into a control terminal TC2 with a delay signal S10 of the delay means 9 as an input; a phase-shifting means 11 for varying a passage phase by an output signal S9 from the second low pass filtering means 8 with an output of the gain variable means 10 as an input to input a variable output signal into a power amplifying means 12 whose distortion should be corrected; a second envelope detecting means 13 for detecting an envelope signal of an output of the power amplifying means 12 whose distortion should be corrected; a subtracting means 14 for detecting a difference between the envelope signal S2 and an envelope signal S14 with the envelope signals S2 and S14 of the first and second envelope detecting means 1, 13 as inputs; a third low pass filtering means 15 for detecting only a DC signal of this subtracting means 14 to feed it back to the control terminal TC1 of the delay means 9; and a correction data memory means 17 for outputting data corresponded to the address, which corrects a change of characteristic due to temperature with the output of digital data S17 in which an output difference signal S15 of the subtracting means 14 is digitalized as an address, characterized in that data corresponding to the address from this correction data memory means 17 is supplied as multiplier of the multiplying means 18.
In accordance with the first-twelfth distortion compensating device of the present invention, a device having an extremely great effect in which predistortion due to digital is carried out without connection of the signal with other than the main path adjacent to the power amplifying circuit and the device does not depend on a mobile phone system is obtained.